There are an estimated 10,000 patients who suffer spinal cord injury (SCI) each year in the U.S. and approximately 250,000 chronic SCI patients. While a primary strategy to repair the spinal cord is to bridge the damage with axons, producing axons of sufficient length and number has posed a significant challenge. Here, we propose to refine and utilize a novel tissue engineering technique to create transplantable nervous tissue constructs for spinal cord repair. This technique was developed in our laboratory through work on the biomechanics of axonal stretch. The key of this procedure is to use a specially designed microstepper motor system to produce continuous mechanical tension on axons spanning two populations of neurons in culture. Using dorsal root ganglia (DRG) neurons, this technique has rapidly produced nerve tracts consisting of up to 106 axons grown at rates of up to 10mm/day and reaching a remarkable 10 cm in length. As such, these axons are of sufficient length and number to bridge even extensive nerve damage. As our core hypothesis, we propose that transplantation of these nervous tissue constructs may create new intraspinal circuits forming relays across spinal cord lesions and improve functional outcome. In our first aim, we will develop nervous tissue constructs composed of stretch-grown axons from fetal rat DRG neurons and encased in carefully selected hydrogels. We will then evaluate the survival and potential integration of these constructs following transplantation into a lesion formed by hemisection of the rat spinal cord. For Aim 2, we will determine the potential clinical applicability of the axon stretch-growth technique by creating nervous tissue constructs composed of adult human and rat stretch-grown DRG axons. The human neurons will come from both live patients and organ donors. Survival and integration of nervous tissue constructs from adult rats will be examined using the rat spinal cord hemisection model. In Aim 3 we will evaluate functional outcome following transplantation of optimized fetal and adult nervous tissue constructs using a model of complete spinal cord transection. If successful, our axonal stretch-growth approach could offer an important alternative, yet complimentary method, to repair the spinal cord by providing laboratory grown 'off-the-shelf living nervous tissue constructs ready for transplant.